1. Field of the Invention
The present invention relates to a flat power cable. The power cable should have adequate current carrying capability and sufficient dielectric strength to minimize electrical losses and failures even under the adverse environmental conditions.
2. Description of Related Art
U.S. Pat. No. 3,889,049, for example, teaches of the conditions within a well. The environmental conditions of the well vary generally depending upon geographical location. In some cases the well fluid is highly corrosive and in many instances well temperatures exceed 275° F. (about 135° C.). Most oil well fluids include brines containing dissolved H2S gas, carbonates and salts, and large volumes of oil. The fluid pressure in wells may be quite high and in many instances exceeds 4,000 psig (about 270 atm). Additionally, the wells are quite deep, averaging 8,000 to 10,000 feet (about 2 to 3 km). The electrical cable must possess sufficient physical strength to allow insertion of the motor and cable to these depths and the outer surface of the cable must resist the abrasion associated with insertion.
Among these applications there are flat submersible electrical cables used to convey electric energy to submersible appliances (i.e. motors) for use in oil, mineral or water wells. The flat shape of these cables allows the passage of the same through narrow ways in oil wells or relatively small diameter, where a larger round cable might cause interference or other problems, as taught, for example, by U.S. Pat. No. 4,600,805.
An example of flat cable used in hostile environment is marketed by the Applicant with the tradename Devilead® Flat Pump Cable. Such cable has three conductors insulated with an EPDM (ethylene propylene diene monomer) based compound. Each insulated conductor is coated by a lead sheath. A lapped steel tape armour encircles the three insulated and sheathed conductors. The presence of said lead-sheath protects the cable insulated conductors against oil, chemicals and gases, and insulation decompression, but also increases the cable weight.
A lighter cable is, for example, marketed by the Applicant with the tradename Deviline® Flat Cable wherein each of the three conductors, insulated by a polypropylene based layer, is protected by a polymeric sheath (based for example, on ethylene propylene diene monomer rubber, EPDM). In turn, the polymeric sheath is helically overlapped with fluoropolymer tape (for example of polytetrafluorethylene PTFE). A lapped steel tape armour encircles the three insulated and sheathed conductors. The combination polymeric sheath/fluoropolymer tape provide the insulated conductors with protection against heat, oil, chemicals and decompression.
The Applicant observed that in high temperature, gas/oil environment or because of change, in pressure, the polymeric sheath tends to swell or enlarge into the interstitial empty spaces under the armour, possibly causing a disarrangement of tapes or braids surrounding the sheath and/or impairing the cable geometry, both the outcomes eventually leading to cable failure. The swelling of the polymeric sheath and the disarrangement of tapes can make the insulated conductors moving one with respect to the other. Under such circumstances, the insulated cores lose their configuration—a highly undesirable occurrence—and this eventually leads to cable failures.
U.S. Pat. No. 7,009,113 deals with a high temperature electrical cable having an interstitial filler and with the problem of improving the roundness of the cable. The electrical cable includes a central insulated conductor and a plurality of outer insulated conductors disposed around the central insulated conductor, the central insulated conductor and the plurality of outer insulated conductors forming a first set of interstices therebetween and the plurality of outer insulated conductors forming a second set of interstices therebetween. The electrical cable further includes a filler material substantially filling at least a portion of the first set of interstices and at least a portion of the second set of interstices and a jacket encasing the conductors and the filler material. Filler material such as a ceramic putty, a fluoroelastomer, and/or a fluorinated grease or oil are exemplified. The electrical cable further includes a yarn strand disposed in at least one of the second set of interstices, a filler material substantially filling at least a portion of the first set of interstices and substantially filling at least a portion of the second set of interstices around the yarn, and a tape layer encasing the conductors, the yarn, and the filler material. In one embodiment, the yarn strand comprises tetrafluoroethylene.
US 2007/0027245 relates generally to the field of oilfield exploration, production, and testing, and more specifically to swellable elastomeric materials and their uses in such ventures. In particular, it describes an apparatus comprising a swellable elastomeric composition with peculiar chemical characteristics. Such apparatus includes those wherein the oilfield element may be any element exposed to water, brine, low and high pH fluids, and/or hydrocarbon fluids, such as, inter alia, seals and insulators used in electrical components, such as wire and cable semiconducting shielding and/or jacketing, power cable coverings.
Another problem faced in the operation of cables positioned in the described hostile environment arise from the presence of low molecular weight hydrocarbons such as methane gas, as disclosed, for example, by U.S. Pat. No. 3,800,066. In the depths of the borehole and at temperatures above 150°, which is quite common, the as can permeate the matrix of the cable due to a phenomenon that may be called activated diffusion.